Process for stretching synthetic threads



United States Patent 8 Claims. in. 2s 72 This invention relates to a process for stretching synthetic threads while they are in a heated condition.

It is well known that the tearing strength and other physical properties of fully synthetic threads, which have been spun from a solution or melt, can be considerably improved by a stretching process. In such a stretching process, the threads are extended or stretched, while at a temperature below their melting point in order to provide permanently lengthened'threads; in the stretching process, there is an orientation of the macromolecules of the thread in the direction of stretching. Since heated threads can generally be stretched more easily and to a greater extent than when they are in the unheated condition, the threads are conventionally conducted across heated surfaces for causing the heating thereof; the heated surfaces are located between the driven input and draw-off stretching rollers, which are driven at different circumferential speeds, means being provided for clamping the threads. A stationary heated strip of metal is conventionally used to form the heating surface, over which the threads slide.

Such hot stretching processes are particularly important in the production of threads for certain technological uses, as for tire cording, since these threads require a high tear strength. Although it is important that a thread be provided with as high a tear strength as possible, it is also highly desirable that the capillary breakage of the threads be reduced.

It is therefore an important object of this invention to provide an improved process for greatly improving the physical properties, and particularly the tear strength, of synthetic threads.

It is also an object of this invention to provide a process for stretching synthetic threads wherein the tear strength of the thread is greatly improved while substantially reducing the capillary breakage of the threads.

It is a further object of this invention to provide a process for stretching synthetic threads, while they are in a heated condition, so that the thread has greatly increased tear strength and reduced capillary breakage.

Further purposes and objects of this invention will appear as the specification proceeds.

Generally, our improved process for stretching synthetic threads, while in a heated condition, includes the steps of passing the thread over a heated surface, drawing the thread from the heated surface at a rate of about 140-280 meters/minute, and substantially freely moving the thread through space for a period of at least about 0.065 second, and preferably for about 0.09-0.30 second; after the lapse of this period of time, the thread passes over the draw-off roller.

This is highly suitable both for stretching of unstretched threads and for the further streching of prestretched threads. It is particularly advantageous to first prestretch the thread by passing it over an unheated element, as a brake prong, thereafter passing the thread over a heated surface, such as a flat iron, and then for a period of time of at least about 0.065 second, freely moving the thread through space before it touches the draw-off roller.

Flat irons being resistance heated have been found to be particularly satisfactory as a heating medium. Stationary heated, brake prongs or brake rollers, however,

it:IIII.IIIIIIIIIIIIII are also suitable. The heating of the thread may also be accomplished by various types of heating elements which engage the thread in succession, preferably in an alternating arrangement, whereby the thread is heated from several sides.

In case the time of free movement is such that the thread must pass through a distance which is difficult for a machine to accommodate, the thread, after leaving the heated surface, may be passed over one or more deflection rollers before it touches the draw-off roller, without seriously affecting the advantages of the process.

Our process has provided excellent results with all known fully synthetic fibers, and particularly good results have been accomplished with polyamide threads. By utilizing our process, it is possible not only to considerably increase the tearing strength with equivalent and even increased tearing extension, but also the quantity of capillary breakage of thread is considerably decreased.

The following examples more fully illustrate the invention, but it is to be understood that the various procedural details included therein are not to be considered as a limitation of the scope of the invention, rather it is intended that all equivalents obvious to those skilled in the art are to be included within the scope of the invention as claimed.

Example I An unstretched, multifile nylon6 thread (Td 4500/ was introduced into a stretching field over an input roller, provided with a contact pressure roller. After a 360 encircling of a brake prong of 10 mm. diameter, it then passed over a 200 mm. long flat iron and was finally drawn oli at 52-fold 180 m./min. speed by a second roller, provided with a distributor roller. The flat iron was at a temperature of 180 C. The running time for the thread from the flat iron to the draw-off roller was 0.15 sec., which corresponds to a running distance of 450 mm.

A comparative experiment was run with a running time of 0.02 sec., corresponding to a distance of 60 mm. The following table compares the results:

TABLE I Running Tearing time strength (EL/den.)

Tearing extension (percent) Capillary breakage number (per 20 km.)

Path (mm) tom Example II For the production of a nylon-66 thread for technical uses, an unstretched thread was first conducted over an input roller, having a distributor roller which served as a clamping point. It was then conducted over a flat iron at a temperature of C. and was drawn off by a second roller at a draw-off velocity of 150 m./min. The running time of the thread from the fiat iron to the drawoff roller was 0.5 sec., which corresponds to a distance of 1250 mm. The stretching ratio caused by the differing circumferential velocity of the rollers was 1:5.4.

A comparative experiment was run with a running time of 0.036, corresponding to a distance of 90 mm. The results are shown in the following table:

TAB LE II Path Running time (sec.)

Tearing strength (g. lden.)

Tearing extension (percent) What we claim and desire to secure by Letters Patent is:

1. A process for stretching synthetic threads between input and draw-off stretching rollers, wherein a heating means is interposed between the stretching rollers, said process comprising the steps of drawing the synthetic thread from the heating means at a rate of about 140-280 meters/minute, and substantially freely moving said thread for at least about 0.065 second before said thread reaches the draw-01f roller.

2. Theprocess of claim 1 wherein said thread is sub-- stantially freely moved for about 0.090.30 second.

3. The process of claim 2 wherein said thread is prestretched before passage to the heating means.

4. A process for stretching synthetic threads, said process comprising the steps of heating said thread, and then substantially freely moving said thread at a speed of about 140-280 meters/minute for at least about 0.065 second, while stretching said thread.

5. The process of claim 4 wherein said thread is prestretched before said heating step and is substantially freely moved for about 0.090.30 second.

6. A process for stretching synthetic threads between input and draw-off stretching rollers wherein a heating means is interposed between the stretching rollers, said process comprising the steps of passing said thread across said heating means to effect heating of said thread, drawing said thread from said heating means at a rate of about 180 meters per minute, and substantially freely moving said thread for about 0.15 second while stretching said thread before said thread reaches the draw-off roller.

7. The process of claim 6 wherein said thread is prestretched before being subjected to the heating step.

8. A process for stretching synthetic thread between input and draw-off stretching rollers wherein a heating means is interposed between the stretching rollers, said process comprising the steps of passing the thread across the heating means to effect the heating thereof, drawing the thread from the heating means at a rate of about meters per minute, and substantially freely moving saidthread for about 0.5 second while stretching said thread before said thread reaches the draw-off roller.

References Cited by the Examiner UNITED STATES PATENTS 2,509,741 5/1950 Miles 2871.3 X 2,993,260 7/1961 Boerma et al. 2871.3X 3,101,990 8/1963 Heighten 28-713 X 3,124,632 3/1964 Larkin et al. 28-71.3 X 3,159,964 12/1964 Kretsch 2871.3 X

DONALD 'W. PARKER, Primary Examiner.

L. K. RIMRODT, Assistant Examiner. 

1. A PROCESS FOR STRETCHING SYNTHETIC THREADS BETWEEN INPUT AND DRAW-OFF STRETCHING ROLLERS, WHEREIN A HEATING MEANS IS INTERPOSED BETWEEN THE STRETCHING ROLLERS, SAID PROCESS COMPRISING THE STEPS OF DRAWING THE SYNTHETIC THREAD FROM THE HEATING MEANS AT A RATE OF ABOUT 140-280 METERS/MINUTE, AND SUBSTANTIALLY FREELY MOVING SAID THREAD FOR AT LEAST ABOUT 0.065 SECOND BEFORE SAID THREAD REACHES THE DRAW-OFF ROLLER. 